The mutagenic and carcinogenic activities of previously untested electrophilic agents were investigated. E. coli WP2(hcr-) and Salmonella TA 1535 and TA 100 were used in standard plate tests to determine the mutagenic activities of several alkyl halides. The ability of alkyl halides and acylating agents to produce lung adenomas in strain A mice was also studied. In general, the alkyl halides were both carcinogenic and mutagenic; branching and ease of dissociation increased both activities. However, the weakly reactive p-alkyl chlorides tended to be mutagenic but not carcinogenic in the systems selected. Except for dimethylcarbamyl chloride, none of the acylating agents studied showed significant carcinogenic activity.